Minimally invasive medical procedures generally employ small diameter instruments that can be inserted directly or through a cannula in a small incision or natural orifice of a patient. Producing small diameter medical instruments that implement the clinically desired functions for minimally invasive procedures can be challenging. For example, many instruments require a small-diameter wrist mechanism that is able to position and manipulate an end effector at the distal end of the instrument. Such wrist mechanisms commonly employ two cables per rotation axis available in the wrist, so that a wrist mechanism providing pitch, yaw, and grip control commonly uses six cables. All of the cables must be routed through the wrist mechanism and back through a small-diameter tube to a transmission, sometimes referred to herein as a backend mechanism. The backend mechanism moves the drive cables as needed to operate the wrist mechanism. Further, some medical instruments have end effectors that require electrical energy, for example, for clinical functions such as desiccation, hemostasis, cutting, dissection, fulguration, incisions, tissue destruction, cauterizing, and vessel sealing. Accordingly, one or more conductors must be routed to the portion of an end effector to be energized, while other portions of the instrument must be insulated from the electrical energy to avoid unintended burning of the patient or a user of the instrument. Fitting all the components of the wrist mechanism, drive cables, and conductive wires into a small diameter, for example, less than about 10 mm, can be difficult.
Minimally invasive medical instruments with lower part counts are desired to facilitate miniaturization of the instrument and to reduce instrument costs.